Tires: Truck tires, proper inflation pressure, mini motorhome

Question
Barry,
I have a Toyota-powered mini motorhome with duallies on the back.  I live in Southern California.  The tires are about 5 years old, and are load range D tires with max load of 1765# at 65 psi.  On my camper, the axle's max load is 3800#, or 950#/tire. I am running 45 psi.  We rarely exceed 65 mph and usually cruise around 55.  Since the tires are way under their max load, can I expect any increase in their longevity?  They still have decent tread.
Thanks,
Art

Answer
Art,

The current thinking in the tire industry is that there is a time limit to tires and some say 6 years and some say 10 years.  I think the difference is the way ambient temperature is considered.  In your case 6 years would be the limit.  BTW the research done on the subject says that it doesn't matter if the tire is used or not - tires seem not be wholly dependent of time, not mileage.

But you need to find the vehicle placard.  It lists the original tire size and the proper inflation pressure for that size.